Debt and Derivative Instruments (Summary of Interest Rate Swap Contracts Outstanding) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($)
Derivative [Line Items]
Derivative instrument, notional amount	$ 217,693
Fair value of derivative assets measured on recurring basis	4,955
Derivative instrument, notional amount	136,795
Fair value of derivative liabilities measured on recurring basis	$ (1,287)
Interest Rate Swap One [Member]
Derivative [Line Items]
Derivative instrument, date entered	Apr. 07, 2015
Derivative instrument, effective date	Apr. 07, 2015
Derivative instrument, maturity date	Apr. 07, 2022
Derivative instrument, pay fixed interest rate	1.74%	[1]
Derivative instrument, notional amount	$ 49,400
Fair value of derivative assets measured on recurring basis	$ 400
Interest Rate Swap Two [Member]
Derivative [Line Items]
Derivative instrument, date entered	Jul. 08, 2015
Derivative instrument, effective date	Aug. 01, 2015
Derivative instrument, maturity date	May 22, 2019
Derivative instrument, pay fixed interest rate	1.43%	[1]
Derivative instrument, notional amount	$ 1,426
Fair value of derivative assets measured on recurring basis	$ 2
Interest Rate Swap Three [Member]
Derivative [Line Items]
Derivative instrument, date entered	Sep. 17, 2015
Derivative instrument, effective date	Sep. 17, 2015
Derivative instrument, maturity date	Sep. 17, 2022
Derivative instrument, pay fixed interest rate	1.90%	[1]
Derivative instrument, notional amount	$ 13,700
Fair value of derivative assets measured on recurring basis	$ 50
Interest Rate Swap Four [Member]
Derivative [Line Items]
Derivative instrument, date entered	Oct. 02, 2015
Derivative instrument, effective date	Nov. 01, 2015
Derivative instrument, maturity date	Nov. 01, 2022
Derivative instrument, pay fixed interest rate	1.79%	[1]
Derivative instrument, notional amount	$ 13,100
Fair value of derivative assets measured on recurring basis	$ 129
Interest Rate Swap Five [Member]
Derivative [Line Items]
Derivative instrument, date entered	Jan. 25, 2016
Derivative instrument, effective date	Feb. 01, 2016
Derivative instrument, maturity date	Feb. 01, 2021
Derivative instrument, pay fixed interest rate	1.40%	[1]
Derivative instrument, notional amount	$ 38,000
Fair value of derivative assets measured on recurring basis	$ 539
Interest Rate Swap Six [Member]
Derivative [Line Items]
Derivative instrument, date entered	Jun. 07, 2016
Derivative instrument, effective date	Jul. 01, 2016
Derivative instrument, maturity date	Jul. 01, 2023
Derivative instrument, pay fixed interest rate	1.42%	[1]
Derivative instrument, notional amount	$ 43,680
Fair value of derivative assets measured on recurring basis	$ 1,569
Interest Rate Swap Seven [Member]
Derivative [Line Items]
Derivative instrument, date entered	Jul. 21, 2016
Derivative instrument, effective date	Aug. 01, 2016
Derivative instrument, maturity date	Aug. 01, 2023
Derivative instrument, pay fixed interest rate	1.30%	[1]
Derivative instrument, notional amount	$ 47,550
Fair value of derivative assets measured on recurring basis	$ 2,108
Interest Rate Swap Eight [Member]
Derivative [Line Items]
Derivative instrument, date entered	Aug. 29, 2016
Derivative instrument, effective date	Oct. 21, 2016
Derivative instrument, maturity date	Dec. 15, 2019
Derivative instrument, pay fixed interest rate	1.07%	[1]
Derivative instrument, notional amount	$ 10,837
Fair value of derivative assets measured on recurring basis	$ 158
Interest Rate Swap Nine [Member]
Derivative [Line Items]
Derivative instrument, date entered	Jun. 27, 2014
Derivative instrument, effective date	Jul. 01, 2014
Derivative instrument, maturity date	Jul. 01, 2019
Derivative instrument, pay fixed interest rate	1.85%	[1]
Derivative instrument, notional amount	$ 24,352
Fair value of derivative liabilities measured on recurring basis	$ (173)
Interest Rate Swap Ten [Member]
Derivative [Line Items]
Derivative instrument, date entered	Jul. 31, 2014
Derivative instrument, effective date	Jul. 31, 2014
Derivative instrument, maturity date	Jul. 31, 2019
Derivative instrument, pay fixed interest rate	1.94%	[1]
Derivative instrument, notional amount	$ 9,561
Fair value of derivative liabilities measured on recurring basis	$ (87)
Interest Rate Swap Eleven [Member]
Derivative [Line Items]
Derivative instrument, date entered	Dec. 16, 2014
Derivative instrument, effective date	Dec. 16, 2014
Derivative instrument, maturity date	May 09, 2017
Derivative instrument, pay fixed interest rate	1.13%	[1]
Derivative instrument, notional amount	$ 10,150
Fair value of derivative liabilities measured on recurring basis	$ (2)
Interest Rate Swap Twelve [Member]
Derivative [Line Items]
Derivative instrument, date entered	Mar. 28, 2014
Derivative instrument, effective date	Mar. 01, 2015
Derivative instrument, maturity date	Mar. 28, 2019
Derivative instrument, pay fixed interest rate	2.22%	[1]
Derivative instrument, notional amount	$ 5,525
Fair value of derivative liabilities measured on recurring basis	$ (81)
Interest Rate Swap Thirteen [Member]
Derivative [Line Items]
Derivative instrument, date entered	Feb. 11, 2015
Derivative instrument, effective date	Mar. 02, 2015
Derivative instrument, maturity date	Mar. 01, 2022
Derivative instrument, pay fixed interest rate	2.02%	[1]
Derivative instrument, notional amount	$ 6,114
Fair value of derivative liabilities measured on recurring basis	$ (32)
Interest Rate Swap Fourteen [Member]
Derivative [Line Items]
Derivative instrument, date entered	May 23, 2014
Derivative instrument, effective date	May 01, 2015
Derivative instrument, maturity date	May 22, 2019
Derivative instrument, pay fixed interest rate	2.00%	[1]
Derivative instrument, notional amount	$ 8,484
Fair value of derivative liabilities measured on recurring basis	$ (89)
Interest Rate Swap Fifteen [Member]
Derivative [Line Items]
Derivative instrument, date entered	May 08, 2014
Derivative instrument, effective date	May 05, 2015
Derivative instrument, maturity date	May 07, 2019
Derivative instrument, pay fixed interest rate	2.10%	[1]
Derivative instrument, notional amount	$ 14,200
Fair value of derivative liabilities measured on recurring basis	$ (177)
Interest Rate Swap Sixteen [Member]
Derivative [Line Items]
Derivative instrument, date entered	Jun. 06, 2014
Derivative instrument, effective date	Jun. 01, 2015
Derivative instrument, maturity date	May 08, 2019
Derivative instrument, pay fixed interest rate	2.15%	[1]
Derivative instrument, notional amount	$ 11,684
Fair value of derivative liabilities measured on recurring basis	$ (158)
Interest Rate Swap Seventeen [Member]
Derivative [Line Items]
Derivative instrument, date entered	Jun. 26, 2014
Derivative instrument, effective date	Jul. 05, 2015
Derivative instrument, maturity date	Jul. 05, 2019
Derivative instrument, pay fixed interest rate	2.11%	[1]
Derivative instrument, notional amount	$ 20,725
Fair value of derivative liabilities measured on recurring basis	$ (269)
Interest Rate Swap Eighteen [Member]
Derivative [Line Items]
Derivative instrument, date entered	Dec. 23, 2015
Derivative instrument, effective date	Dec. 23, 2015
Derivative instrument, maturity date	Jan. 02, 2026
Derivative instrument, pay fixed interest rate	2.30%	[1]
Derivative instrument, notional amount	$ 26,000
Fair value of derivative liabilities measured on recurring basis	$ (219)

[1] Receive floating rate index based upon 1 month LIBOR. At March 31, 2017, the 1 month LIBOR was 0.98%.